Despite the sustained efforts of numerous groups to develop immune approaches for the treatment of cancer, thus far, the therapeutic responses have been disappointing. The reasons for this failure remain unknown. Thus, in the current study we propose to study the role of T-cell maturation stage in determining T-cell susceptibility to tumor-induced suppression by alterations in TGF-b susceptibility. Memory and effector CD8+ T cells are functionally more responsive than naive cells. Thus, we hypothesized that memory and effector T cells were less susceptible to tumor-induced suppression than naive cells. Paradoxically, we found that effector CD8+ T cells were considerably more susceptible to tumor-induced suppression than naive cells (90% vs. 30%). Our data suggest that adoptive transfer of in vitro activated effector CD8+ T cells may be ineffective due to increased CD8+ T-cell susceptibility to tumor-induced suppression. Regarding the mechanisms responsible for this disparate effect, we found that TGF-b was a key molecular mediator of suppression, and expression of transcriptional regulators of TGF-b signaling (Smad4 and TGF-bRII) correlated with T-cell status and susceptibility to suppression. Based on these observations, we propose the following hypothesis: CD8+ T-cell maturation status (naive, effector and memory) determines susceptibility to tumor-induced suppression, with effector and memory T cells being more susceptible to suppression than naive T cells, due to increased responsiveness to TGF-b. In order to evaluate antigen specific CD8+ T-cell responses, we will use CD8+ T cells from transgenic mice expressing a CD8+ TCR against gp100/pmel (a self antigen naturally expressed by normal melanocytes and melanoma cells) and a non-self antigen, chicken ovalbumin (OT-I). 1) We will examine the susceptibility of naive, effector and memory CD8+ T cells to TGF-b in vitro, and whether expression of TGF-bRII and Smads correlates with susceptibility to suppression. 2) We will evaluate the in vivo suppressive effect of tumor disseminated disease (early and established) on naive, effector and memory CD8+ T cells, and the effect of depleting suppressor cells or blocking TGF-b on naive, effector and memory CD8+ T-cell responses. 3) We will study whether interfering with TGF-b signaling in vivo in CD8+ T cells evenly rescues naive, effector and memory TCR transgenic CD8+ T cells from tumor-induced suppression. Narrative The results of T-cell based immune therapeutic approaches against cancer based on adoptive cell transfer and vaccination, thus far, have been disappointing for reasons that remain unknown. Thus, in the current study we propose to study the role of T-cell maturation stage (naive, effector and memory) in determining T-cell susceptibility to tumor-induced suppression by alterations in TGF-b susceptibility.